As is well known, dental casting alloys should provide a high degree of biocompatibility or inertness to the conditions in the mouth and good physical properties so that they will provide long lived usage. In addition, those alloys which are used to provide castings upon which porcelains may be cast must provide good bonding characteristics to the porcelains and other characteristics which are compatible with the porcelain, such as similar coefficient of expansion, avoidance of discoloration of the porcelain, etc. Lastly, the alloy should process well during casting and work with commercially available porcelains.
Until recent years, gold alloys, usually gold/platinum alloys, have been preferred as dental casting materials because they have provided a highly desirable balance of properties. The commercially available dental porcelains have been formulated so as to be compatible therewith.
Recently, the escalating costs of gold and platinum have resulted in extensive efforts to find alternate alloy compositions which would afford acceptable properties at considerably lower cost. Base metal alloys have generally been found to suffer from one or more limitations such as lack of sufficient biocompatibility, lack of aesthetics, etc. As a result, over the last several years, there has been considerable activity in the development of palladium base alloys and palladium/silver alloys in an effort to make use of the nobility of lower cost palladium. The silver has generally served to reduce cost still more and modify the thermal coefficient of expansion.
As a result, palladium/silver alloys have been developed which simulate the appearance of platinum alloys and which provide a high degree of biocompatibility with useful casting and physical properties. However, the silver content has a tendency to oxidize at the firing temperature and to discolor the porcelains which are fired thereon to provide the aesthetic coatings which are widely employed, particularly with anterior dental restorations.
It is an object of the present invention to provide a palladium/silver dental alloy which is especially adapted for use with dental porcelains and which exhibits a highly desirable balance of casting properties, physical properties, biocompatibility and freedom from discoloration of porcelain coatings which are fired thereon.
It is also an object to provide such an alloy which is relatively low cost when compared to gold and platinum alloys and which affords properties which are comparable thereto.
Another object is to provide such an alloy which may be processed relatively readily and which will provide excellent bond strengths for porcelain coatings fired thereon.